AD73322LYRU Analog Devices Inc, AD73322LYRU Datasheet - Page 30

• Manufacturer Part Number: AD73322LYRU
• Description: IC ANALOG FRONT END DUAL 28TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD73322LYRU

• Rohs Status: RoHS non-compliant
• Number Of Bits: 16
• Number Of Channels: 4
• Power (watts): 73mW
• Voltage - Supply, Analog: 2.7 V ~ 5.5 V
• Voltage - Supply, Digital: 2.7 V ~ 5.5 V
• Package / Case: 28-TSSOP

AD73322L
In the case of voice-band processing where 4 kHz represents the
Nyquist frequency, if the signal to be measured were externally
band-limited, then an 8 kHz sampling rate would suffice.
However, if the bandwidth must be limited with a digital filter,
then it may be more appropriate to use an initial sampling rate
of 16 kHz and to process this sample stream with a filtering and
decimating algorithm to achieve a 4 kHz band-limited signal at
an 8 kHz rate. Figure 19 details the initial 16 kHz sampled tone.
Figure 29 shows the spectrum of the final 8 kHz sampled
filtered tone.
ENCODER GROUP DELAY
When programmed for high sampling rates, the AD73322L
offers a very low level of group delay, which is given by
where:
Order is the order of the decimator (= 3)
M is the decimation factor (= 32 @ 64 kHz, = 64 @ 32 kHz,
T
DEC
= 128 @ 16 kHz , = 256 @ 8 kHz)
DMCLK = 16.384 MHz)
Group Delay (Decimator) = Order × ((M − 1)/2) × T
is the decimation sample interval (= 1/2.048e6 based on
–100
–120
–140
–100
–120
–140
–20
–40
–60
–80
–20
–40
–60
–80
Figure 29. FFT (ADC 8 kHz Filtered and Decimated from 16 kHz)
0
0
0
0
1000
Figure 28. FFT (ADC 16 kHz Direct Sampling)
500
2000
1000
3000
1500
FREQUENCY (Hz)
FREQUENCY (Hz)
4000
2000
5000
2500
6000
3000
7000
3500
8000
4000
DEC
Rev. A | Page 30 of 48
Consider a second example:
If final filtering is implemented in the DSP, the final filter’s
group delay must be taken into account when calculating
overall group delay.
DECODER SECTION
The decoder section updates (samples) at the same rate as the
encoder section. This rate is programmable as 64 kHz, 32 kHz,
16 kHz, or 8 kHz (from a 16.384 MHz MCLK). The decoder
section represents a reverse of the process that was described in
the encoder section. In the case of the decoder section, signals
are applied in the form of samples at an initial low rate. This
sample rate is then increased to the final digital sigma-delta
modulator rate of DMCLK/8 by interpolating new samples
between the original samples. The interpolating filter also has
the action of canceling images due to the interpolation process
using spectral nulls that exist at integer multiples of the initial
sampling rate. Figure 30 shows the spectral response of the
decoder section sampling at 64 kHz. Again, its sigma-delta
modulator shapes the noise so it is reduced in the voice
bandwidth dc–4 kHz. For improved voice-band SNR, the user
can implement an initial anti-imaging filter, preceded by 8 kHz
to 64 kHz interpolation, in the DSP.
Group Delay (decimator @ 64 kHz) = 3 × (32 − 1)/2 ×
(1/2.048e6) = 22.7 µs
–100
–10
–20
–30
–40
–50
–60
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–80
–90
0
0
0.5
Figure 30. FFT (DAC 64 kHz Sampling)
1.0
FREQUENCY (Hz)
1.5
2.0
2.5
3.0
×10
3.5
4